Novel erythropoietin stimulating-protein (NESP) is a hyperglycosylated erythropoietin analog having five changes in the amino acid sequence of rHuEPO which provide for two additional carbohydrate chains. More specifically, NESP contains two additional N-linked carbohydrate chains at amino acid residues 30 and 88 (numbering corresponding to the sequence of human EPO)(see PCT Application No. US94/02957, herein incorporated by reference in its entirety). NESP is biochemically distinct from EPO, having a longer serum half-life and higher in vivo biological activity; Egrie et al., ASH 97, Blood, 90:56a (1997). NESP has been shown to have ˜3 fold increase in serum half-life in mice, rats, dogs and man; Id. In mice, the longer serum half-life and higher in vivo activity allow for less frequent dosing (once weekly or once every other week) compared to rHuEPO to obtain the same biological response; Id.
A pharmacokinetic study demonstrated that, consistent with the animal studies, NESP has a significantly longer serum half-life than rHuEPO in chronic renal failure patients, suggesting that a less frequent dosing schedule may also be employed in humans; MacDougall, et al., J American Society of Nephrology, 8:268A (1997). A less frequent dosing schedule would be more convenient to both physicians and patients, and would be particularly helpful to those patients involved in self-administration. Other advantages to less frequent dosing may include less drug being introduced into patients, a reduction in the nature or severity of the few side-effects seen with rHuEPO administration, and increased compliance.
Although the extended half-life of NESP offers the advantage of less frequent dosing relative to EPO, there are still potential indications, such as chemotherapy, which may require an even longer therapeutic half-life than NESP currently demonstrates.
A common approach often used to extend the half-lives of proteins in vivo is the chemical conjugation of a water soluble polymer, such as polyethylene glycol (PEG), to the protein of interest. Generally, polyethylene glycol molecules are connected to the protein via a reactive group found on the protein. Amino groups, such as those on lysine residues or at the N-terminus, are convenient for such attachment.
A variety of approaches have been used to attach the polyethylene glycol molecules to the protein (PEGylation). For example, Royer (U.S. Pat. No. 4,002,531) states that reductive alkylation was used for attachment of polyethylene glycol molecules to an enzyme. Davis et al. (U.S. Pat. No. 4,179,337) disclose PEG:protein conjugates involving, for example, enzymes and insulin. Shaw (U.S. Pat. No. 4,904,584) disclose the modification of the number of lysine residues in proteins for the attachment of polyethylene glycol molecules via reactive amine groups. Hakimi et al. (U.S. Pat. No. 5,834,594) disclose substantially non-immunogenic water soluble PEG:protein conjugates, involving for example, the proteins IL-2, interferon alpha, and IL-1ra. The methods of Hakimi et al. involve the utilization of unique linkers to connect the various free amino groups in the protein to PEG. Kinstler et al. (U.S. Pat. Nos. 5,824,784 and 5,985,265) teach methods allowing for selectively N-terminally chemically modified proteins and analogs thereof, including G-CSF and consensus interferon. Importantly, these modified proteins have advantages as relates to protein stability, as well as providing for processing advantages.
PEGylation approaches such as those described above are traditionally applied to non-glycosylated proteins derived from bacterial expression systems in order to render improvements in solubility and in vivo circulating half-lives (such properties are typically conferred to glycosylated proteins (glycoproteins) through the carbohydrate moieties added in the course of eukaryotic expression). The effects of PEGylation on the in vivo half-lives of non-glycosylated proteins is generally thought to derive from the physicochemical and dynamic properties of PEG conferring a larger hydrodynamic volume and total mass to the conjugate, thus reducing the rate of renal clearance. Additional benefits typically include increased solubility and decreased immunogenicity for the conjugate. However, not all proteins respond equally to PEGylation and there is no guarantee of improved performance.
The present invention is based upon the surprising finding that a highly glycosylated protein, e.g., NESP, can be PEGylated to provide a pharmaceutical composition with an even more dramatic sustained duration profile than NESP, allowing for a once every 4–6 week dosing for raising hematocrit and treating anemia, and thus providing tremendous therapeutic advantage.